2-Ethylhexyl p-methoxycinnamate, 1, is a known sunscreen agent which absorbs ultraviolet radiation in the UV-B range. ##STR1## The ester may exist as the E- or Z-isomer or as a mixture of these isomers.
There are two major processes for the manufacture of 2-ethylhexyl p-methoxycinnamate. The first involves condensation of p-methoxybenzaldehyde with the acetate of 2-ethylhexanol as follows: ##STR2## The second involves condensation of p-methoxybenzaldehyde with methyl acetate followed by a transesterification with 2-ethylhexanol, as follows: ##STR3## In either case the crude material is usually distilled in order to separate the desired product 1 from other reaction materials in the crude material such as unreacted starting material. Another purpose of the distillation step is to obtain material which is free from undesirable odors since the ester 1 is used predominately in cosmetic and sunscreen preparations applied directly to the skin.
It has been reported recently that certain samples of this ester can test positive in the Ames test. [See for example A. M. Bonin et al., Mutation Research 105 (1982), 303-308.] The Ames test is a procedure developed by Ames et al. to screen chemicals for potential mutagenicity. [See for example B. N. Ames et al., Mutation Research 31 (1975), 347-364.] The test specimen is a bacterial defective mutant which is known to revert to the normal mutant (wild type) under the influence of mutagens.
A. M. Bonin et al., loc. cit., expressed the theory that a trace component which is sometimes present in the 2-ethylhexyl p-methoxycinnamate may be responsible for the occurence of an Ames positive reaction. Its nature or existence is, however, unreported. A need exists, therefore, to find a method which insures that any 2-ethylhexyl p-methoxycinnamate which is produced for sale and use will not test positive when subjected to the Ames test. The invention described herein fills that need.